Russell, Henry Norris (1877–1957)

American astronomer who, independently of Ejnar Hertzsprung,
realized the relationship between a star's temperature (color) and its brightness,
and designed a diagram illustrating this relationship in 1913, later called
the Hertzsprung-Russell diagram. Russell
spent six decades at Princeton University – as student, professor,
observatory director (1912–47), and active professor emeritus. From
1921 on he also made lengthy annual visits to Mount
Wilson Observatory. He measured parallaxes
in Cambridge, England, with A. R. Hinks and found the correlation between
spectral types and absolute
magnitudes of stars that is partly named after him. He popularized the
distinction between giant stars and dwarfs while developing an early theory
of stellar evolution. With his student, Harlow Shapley,
he analyzed light from eclipsing binary
stars to determine stellar masses. Later he and his assistant, Charlotte
Moore Sitterly, determined masses of thousands of binary stars using statistical
methods. With Walter Adams, Russell applied
Meghnad Saha's theory of ionization to stellar atmospheres and determined
elemental abundances, confirming Celia Payne-Gaposchkin's
discovery that the stars are composed mostly of hydrogen. Known as the "Dean
of American astronomers," Russell was a dominant force in the community
as a teacher, writer, and advisor.

In the 1920s, Russell was persuaded by the Jeans-Jeffreys
tidal hypothesis to affirm that planetary systems are "infrequent" and
inhabited planets "matters of pure speculation." Two decades later, however,
on the back of independent claims by Frank Schlesinger at Yale and Kaj Strand
at the Sproul Observatory of the discovery
of planetary systems around two nearby stars (later demonstrated to be unfounded),
he declared that it was time to reverse this view and consider that there
may be a very large number of extrasolar worlds.1 Regarding our
planetary neighbors, Russell, in the 1920s and '30s, considered Venus
almost certainly non-biological but Mars the
possible abode of vegetation and other low forms of life.